1. Field of the Invention
This invention relates to ink jet print heads, and in particular to an edge-shooter ink jet in-line print head, and a method for manufacturing the print head. Print heads of this kind are preferably used in small, fast printers as they are utilized, for instance, in franking machines for franking postal matter.
2. Description of the Related Art
Ink jet print heads built on the edge-shooter or face-shooter principles (First Annual Ink Jet Printing Workshop, Mar. 26-27, 1992, Royal Sonesta Hotel, Cambridge, Mass.) are known in the art.
So far, efforts have been made to minimize chamber dimensions in an effort to increase nozzle density. Also, nozzle chambers have been arranged concentrated to the face edge. However, this principle is useful only for ink jet modules with few nozzles in one row and not when there is a high number of nozzles or a high packing density.
In a first generation of ink jet print heads, the same were built according to the edge-shooter principle of single impulse jets which comprise an elongated ink chamber with a rectangular cross-section and a piezo crystal located thereabove (BIS CAP Ink Jet Printing Conference, Monterey, Calif., Nov. 11-13, 1991).
In a later generation, a nozzle panel was disposed in front of a one piece ink jet print head with several chambers. In that case, the chambers do not lie in parallel and side by side with the smaller chamber surface but with the larger chamber surface. Piezo crystals thereby form the chamber walls. This is referred to as the "shared wall concept" (Ink Jet Printing Conference, Nov. 11-13, 1991).
German patent No. DE 34 45 761 A1 discloses a process for manufacturing a transducer arrangement from a single plate of a transducer material. After coating the lower plate surface with a membrane layer, a removal of material from the upper surface follows, creating separated areas arranged on the membrane above each pressure chamber (area 25.4 mm by 2.54 mm). It is no longer necessary to provide an adhesive connection between the transducer material and the membrane, with the regularity of all distances and spacings being improved. The resulting nozzle distance, however, becomes comparatively large.
Moreover, from U.S. Pat. No. 4,680,595 to Cruz-Uribe et al., a face-shooter type print head which has a doubled nozzle density with two groups of ink chambers is known. Each print chamber is rectangular in cross section and includes a supply channel and a nozzle as well as an oscillation plate with a piezo-ceramic element. However, this print head is disadvantageous in that pressure waves occurring in the ink supply and in each chamber can result in a spillover to other pressure chambers. This spillover may only be eliminated by providing for extensive supplementary safeguards. Another disadvantage is that these ink jet print heads must be manufactured in an expensive large-scale manufacturing process.
From U.S. Pat. No. 4,703,333 to David Hubbard, it is known to produce an ink jet print head from a number of face-shooter modules which are diagonally staggered, one on top the other, resulting in a configuration which is inclined towards the surface of a recording medium. Ink jet print heads having such an inclined configuration produce a constant recording even if the thickness of the recording medium varies. However, production of such print heads requires a multitude of process steps and it is difficult to guarantee in a large-scale process the accuracy required for each print head arrangement. The electrical control for these print heads during use is a further difficulty.
The doubled nozzle density in one row obtained with the face-shooter ink jet module, which has two groups of ink chambers arranged symmetrically with regard to the nozzle row has not been, up to now, obtainable with edge-shooter ink jet modules having one nozzle row. For edge-shooter ink jet modules, several nozzle rows are typically arranged both horizontally and vertically staggered in order to obtain double mapping density.
A staggered configuration of two rows of nozzles in an edge-shooter module is known (First annual ink jet printing workshop, Mar. 26-27, 1992, Royal Sonesta Hotel, Cambridge, Mass.). The module usually consists of only three members in total, typically made from glass, namely a center member with openings and two side parts each having one row of ink chambers and a nozzle row at respective edges of the side members. The two rows of ink chambers and nozzles are offset relative to one another, and consequently possess the disadvantages already mentioned with respect to module assembly and electrical control.
These disadvantages are further aggravated in an ink print head comprising several of these modules. It is important, in this respect, that the staggering of individual nozzle rows be exactly the same. Furthermore, each module had to be connected to an ink storage tank via separate ink supply conduits and filters.
In the staggered configuration of two rows, of which each have a low nozzle density, the minimum spacing between adjacent nozzles in each row may not be reduced more than the minimum size required for the ink chambers.
Due to manufacturing process limitations, it is impossible to obtain a steady nozzle size for all nozzles, because channels are etched into several individual glass parts. Even minor differences in size or material can result in deviations of nozzle shape or position.
It is accordingly an object of the invention to provide an ink jet print head and a method for manufacturing the same, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and to provide an ink jet print head with a high nozzle density per row and a manufacturing process for the print head with low production costs.